Scavenging two-cycle engine



u 937. E. B. POLLISTER I 2,090,149

SCAVENGING TWO-CYCLE ENGINE I Filed Oct. 9, 1931 wmm INVENTOR.

BMW/W A TTORNEYS.

Patented Aug. 1?, i937 UNHTED STATES FA'EENT @EFHQE SCAVENGING TWO-CYCLE ENGKNE Application October 9, 1931, Serial No. 567,824

1 Claim.

The object is to improve the scavenging and air-charging process in high speed internal combustion engines, particularly high speed two-cycle injection-type engines and the invention consists 5 in the means and method herein disclosed for utilizing the scavenging air, from a single source, with greater scavenging efficiency than heretofore possible.

The principle of the invention is exemplified by 10 the accompanying drawing, in which- Fig. 1 represents in simple diagram one cylinder of a multi-cylinder engine incorporating said principle, being in central Vertical section.

Fig. 2, a vertical section on line IIII of 15 Fig. 1;

Fig. 3, a section on line III-III of Fig. 2.

These figures will be understood to be diagrams merely. The cylinder l, piston 22, exhaust ports 3, lower tier of air ports 4, upper tier of air ports 5,

all will be recognized as of common design without description and it will be understood that in its down or working stroke the piston first uncovers the upper tier of air ports 5, next the exhaust ports 3 and then the lower tier of air 25 ports 4, and the reverse on compression. The engine may be assumed to have a fuel injection device as indicated at the top of the cylinder.

Air is supplied to both tiers of air ports from a main horizontal header or receiver 6 which may L be the common supply for all the cylinders of the engine and to which air is supplied by any suitable source, for instance an air blower as indicated at l driven by the engine itself or otherwise, and preferably by electric motor, and

adapted in its normal operation to maintain an air pressure of say 2 lbs. in the receiver, more or less according to conditions.

From the receiver air may pass to the upper tier of air ports 5, through the bank of pivoted shutz g' ters 8 which open inwards or toward the cylinder but close against each other to prevent any opposite flow. These shutters constitute an automatic air inlet valve for the scavenging air, that is a valve which is self-opening by the air itself, 45 and serves to pass air into the cylinder whenever the piston uncovers the air ports 5 and the pressure then obtaining in the cylinder is less than the air pressure in the receiver. From the receiver 6 air may also pass through the restricted 50 slot or passage 9 to an accumulator or expansion chamber lil individual to each cylinder and intervening between the receiver and the lower tier of air ports 6. This chamber and the restricted passage are indicated as produced by the appli- 65 cation of a plate it partly over the entrance to the normal communication passage between the receiver and the ports 4 in the cylinder wall; this passage being formed by walls projecting more or less tangentiallyfrom the cylinder wall and at right angles to the axis of the cylinder, the space within the chamber is wider near its ends than at its center, as appears in Fig. 3. As appears from the drawing, the capacity of this chamber, that is to say the space enclosed within the walls forming it, is considerably greater than the total capacity of the air ports i it serves. While the air ports l are covered and closed by the piston, air flows into the chamber Ill from the receiver until the presure therein substantially equals whatever pressure is maintained in the receiver, say to 2 lbs. When the descending piston begins to open said ports, the exhaust ports being then open, the accumulated air blows out of the chamber into the cylinder with a quick pufi. Thereafter while said ports remain uncovered, the flow of air from the receiver to the cylinder is throttled by reason of the restriction represented by the slot or passage 9 so that the air pressure in the chamber H] is less than the receiver pressure, being reduced to half that pressure or less, say one pound, this being due to the fact that the restriction to flow represented by the slot 9 is greater or not less than the restriction represented by the several air ports 4. the area of the slot being less than the sum of the areas of the outlets from the ports 4 at least during the major part of the open period of the latter. However, it will be observed from these figures that the slot is large enough to admit air to the accumulator or expansion chamber, throughout the major portion of the scavenging period, at substantially the same rate as air flows from the chamber to the cylinder, so that after the first quick puff of high pressure air from the chamber, low-pressure scavenging air flows through the ports t as though the chamber were absent and in substantially the same manner as it has been customary to supply low-pressure scavenging air to engines heretofore. But during this low pressure flow through the lower ports, the air entering the cylinder through the upper ports 5 is under the constant and higher pressure maintained in the receiver by the blower, that is 2 lbs. in the case taken for example, and enters at a corresponding rate, as will be understood, while the exhaust ports remain open and thereafter until the ascending piston closes said ports or thepressureshave become balanced. The result of this operation is that the quantity of air entering the cylinder through the upper tier of ports is relatively increased, or conversely stated, that the quantity passing the lower ports is relatively decreased, as compared to the same organization without the throttling slot and accumulator chamber, and this means that the pressure and quantity of air necessary to produce proper scavenging action through the upper ports ucts correspondingly expensive of power, but by the use of the accumulator chamber scavenging is well accomplished without resorting to excessive air pressure nor the special blowing apparatus for producing it. The virtue of the puff of air lies in that it helps to overcome the initial inertia of the air in the receiver so that its flow starts sooner than would otherwise be the case. It will be understood that whereas the air supply above described has been referred to as scavenging air, it is also charging air, or super-charging air acaccording to its pressure relation to the cylinder contents.

I claim:

The combination in a two-cycle engine having upper and lower tiers of air admission ports and exhaust ports all controlled by the piston, of a horizontal air receiver extending alongside said tiers of air ports, an accumulator chamber constituted by the space between said receiver and the cylindrical wall in which said tier of lower air ports is formed, said space being wider near its ends than at its center and of considerable volume, an automatic air valve intervening between the air receiver and the upper air ports, the entrance to said accumulator chamber offering greater resistance to air flow than the lower tier of air ports, whereby the initial discharge from such ports is at full receiver pressure followed by scavenging flow at the reduced pressure permitted by said entrance.

EDWARD B. POLLISTER. 

